In the field of petroleum drilling, it is often necessary, to actuate from a distance tools or equipments placed in the wellbore.
According to the prior art, an annular piston having two faces and a throttle element including a needle-flow bean of variable opening area are used. One face of this piston is subjected to the pressure forces prevailing on one side of the throttle elememt, the other face being subjected to the pressure forces on the other side of the throttle element.
The flow bean is generally borne by the piston and the needle is fastened to a pipe containing the assembly and in which the piston can move to perform the desired actuation. The piston includes return means which keep it in a position of rest corresponding to a relatively large opening area of the throttle element, leading to a low pressure drop for working flow rates.
When one wishes to actuate the equipment, the flow rate is increased, which increases the pressure drop on either side of the throttle element and the piston therefore tends to move by acting against the return means. During this motion, the flow bean enters the throttle element increasingly deep, hence a higher increase in the pressure drop providing the power for actuating the equipment.
The prior art may be illustrated by patent FR-2,575,793.
However, such a device lacks precision concerning the flow rate threshold leading to the actuation initiation. In fact, the assembly consisting of the piston and the return spring, which must react to or transmit high powers, cannot be precisely sensitive to a given flow rate threshold, for example because of frictional stresses.
Furthermore, this device works through a flow rate increase with respect to the working flow rates. Now, drilling conditions may prevent such a flow rate increase. In fact, the increase due to pressure drops downstream from the device may lead to fracturations in the formation or destabilize the walls of the well, whereby the operation safety may be questioned. Besides, a power increase with respect to the power used for drilling is often impossible because the pumping equipment already frequently works at full power for the drilling operation itself.
Patent FR-2,641,320 solves the problem of the flow rate threshold precision by using a flow bean or a needle borne by the piston, but mobile with respect to this piston.
This flow bean or this needle, of small size compared to the piston and equipped with appropriate return means, is precisely sensitive to a flow rate threshold. However, actuation still presents the major drawback of being initiated by a flow rate increase with respect to working flow rates.
Application FR-2,670,824 also describes a known device allowing the two problems to be solved by using a needle-flow bean system or an equivalent. This device allows notably actuation to be initiated from a flow rate threshold lower than or equal to working flow rates, while providing a high activation force such as that necessary for actuation.
Document FR-2,670,824 filed by the applicant discloses an actuating device in which the partial throttling system of the fluid passageway is adjusted according to two positions: an actuation position and a position called a drilling position where no actuation is possible. Adjustment is either remote controlled from the surface, or occupies successively the two positions by using an appropriate operational sequence. This device presents the drawback of requiring a complex remote drive or, in the other case, of having a method of operation which gives no reliable information on the real position of the throttling system.
The present invention widely solves the drawbacks cited above by using a fluid passageway throttling system which is adjusted by the hydrodynamic action of the fluid and by an improved system for controlling the adjusting means, allowing the operator to be certain of being either in the drilling position, or in the equipment activation position.